1. Field of the Invention
The present invention relates to a laser area sensor that detects, for example, an intruder or the like in the building premises. In particular, the present invention relates to a laser area sensor in which reliability of detecting an intruder or the like by the laser area sensor can be maintained even in bad weather conditions.
2. Related Art
Conventionally, as one type of crime prevention apparatuses, a microwave sensor is known that transmits microwaves toward a detection area, and, if an intruder is present in the detection area, receives waves reflected by the intruder and detects the intruder.
Also, a ‘security system’ for detecting an intruder using a laser range finder that adopts laser light as a light source instead of microwaves has been proposed (see Japanese Patent No. 3011121 (hereinafter, referred to as ‘Patent Document 1’), for example).
This ‘security system’ comprises: a sensor portion that sets a monitored area according to a scanning angle at which two-dimensional scanning is performed with light of an optical range finder, and, if an intruder within the area is detected, outputs distance data and angle data of the intruder; a swivel camera portion that is disposed on an electrically-driven swivel base and swivels in conjunction with the sensor portion; and a control portion that has a function to detect whether or not an intruder is present upon a plurality of successive changes in the distance data or the angle data detected by the sensor portion, calculate the position of the intruder based on the changed distance data and angle data from the sensor portion, swivel the swivel camera portion of the electrically-driven swivel base according to the positional data, and display image data of the intruder on a monitor.
Although slightly different from crime prevention apparatuses or security systems, an ‘object identifying method using an area sensor’ that can accurately identify a pedestrian or the like using laser light also has been proposed (see JP 2004-185363A (hereinafter, referred to as ‘Patent Document 2’), for example).
According to this ‘object identifying method using an area sensor’, the light reflection time is measured in scanning performed by causing pulsed laser light to be projected by an area sensor comprising a laser sensor to a detection area that includes a walking area in which pedestrians are guided and an area around the walking area, a difference between the reflection time when no object is present and the reflection time when an object is present is obtained for each scanning point, thereby calculating the shape and the size of the object, and a vector obtained by a change in the position of the object in each scanning, and an object that moves in the guide direction in the walking area and an object that moves in a direction cutting across the walking area are identified based on calculated signals.
However, with a laser range finder used in a security system as in Patent Document 1 above and a laser sensor used in an object identifying method using an area sensor as in Patent Document 2 above, the laser light may be reflected or attenuated by, for example, rain, snow, dense fog or the like during bad outdoor weather conditions, interfering with accurate detection of an intruder or the like.